This invention relates to intravascular implants for maintaining vascular patency in humans and animals. The present invention comprises an open-ended wire formed device of basically cylinrical shape and made of a softer-then spring type metal and fitted over an inflatable element of a typical balloon type catheter such as described in U.S. Pat. No. 4,195,637 and U.S. Pat. No. 4,402,307. The wire formed device is intended to act as a permanent prosthesis stent and is implanted transluminarely. Specifically, this invention is characterized by the ability of said intravascular stent to be enlarged radially after having been introduced percutaneously, transported transluminarely and positioned at desired location. In additiona, this invention relates to a method whereby a permanent prosthesis stent is implanted at the same time the angioplasty procudure is being performed. This invention is particularly useful in transluminar implantation of a stent in the field of cardiology and especially in the case of coronary angioplasty to prevent restenosis.
In my U.S. Pat. No. 4,649,992 a device is described in combination with a catheter which is basically a compression spring retained between a partially inflated balloon and an abuttment immediately behind the balloon on the catheter shaft. The intent is to transport the spring prosthesis in this manner to the desired location and then after a successful angioplasty procedure release said spring prosthesis by totally evacuating said balloon, thus allowing said spring prosthesis to expand linearly and stay in place while the balloon catheter is withdrawn. This method is quite simple and its simplicity is very attractive, however, it has some drawbacks. One and foremost is the fact that the spring has a fixed diameter and as such is unable to fully conform to the inside wall of the vessel which at times is quite tortuous and thus could conceivably create a somewhat turbulant flow of blood, and possible thrombosis could in some cases result. Other patents, e.g. U.S. Pat. No. 4,553,545 teaches a different method where a relatively complex mechanical rotating device and co-axial cables are employed to achieve the necessary means to change the diameter of the implanted stent to a larger dimension at the point of implant. Still other patents, e.g. U.S. Pat. No. 3,868,956 describes a method wherein a temperature responsive metallic device is used and expanded after implant using external heat sources. All of the above mentioned devices present drawbacks of various magnitudes including blood coagulation and possible thrombosis and considerable complexity of procedure.
In angioplasty procedures at this time, in many cases restenosis occurs soon thereafter, which requires a secondary procedure or a surgical bypass operation. The implanted prosthesis as described herein will preclude such additional procedures and will maintain vascular patency indefinitely.
Depending on the size used, the stent according to this invention can also be efficacious in other similar applications, such as: repairs of aneurysms, support of artificial vessels or liners of vessels, initial repairs of dissections and mechanical support to prevent collapsing of dialated vessels. Still many other and similar applications will be satisfied by this invention without departing from the basic prewise and concept.
This stent and the metod of its use particularly allows a single procedure to combine the essential angioplasty and a simultaneous implant of a permanent prosthesis designed and intended to prevent restenosis and further complications arising therefrom, also reducing the risk factor and trauma for the patient.
Another use of stents is for aortic dissection.
In the case of aortic dissection, especially a type III dissection of the descending aorta, there is no intravascular stent or prosthesis available, which is both long and flexible enough to repair a typical dissection extending the entire length from the point of origin down to the aortic bifurcation. Also, for the repair of the most difficult and most dangerous dissection, namely the type I which is that of the ascending aorta and the aortic arch, no stent is available today which could be used and be implanted intraluminarely for non-surgical repair of such a dissection. Most intravascular prosthesis and stent available today are of limited length and diameter and are especially limited in terms of flexibility and more specifically in terms of longitudinal flexibility unable to conform to tight bends and adhere to the walls of the intima and at the same time be flexible to stretch and move with each heartbeat such as experienced in the aortic arch.
Therefore, most such cases are treated medically. If surgery is necessary, it often requires the use of hypothermia and cardiopulonary bypass. Surgical procedures of this type involve high risk to the patient, a highly skilled team of cardiovascular surgeons and sophisticated equipment, because it requires the replacement of the affected region with an interpositional graft. High mortality and morbidity are associated with surgery in this region. This is especially true for the elderly and other poor candidates for a major surgery. The cost associated with such a surgical procedure is also very high.
Prior to the development of this invention, there has been no intravascular stent which would satisfy the following conditions necessary to contemplate a non-surgical repair of a dissecting aorta:
a) To be long enough to extend from the base of the aortic arch down to the aortic bifurcation.
b) To be flexible longitudinally throughout its length.
c) To be radially expandable easily, a small section at a time using common dilatation balloon or similar expanding device designed for that purpose.
d) To be radially expandable to various diameters and to conform to tortuous conditions of a diseased aorta.
e) To be non-obstructive to all branches.
f) To be clearly visible on Floroscope both during deployment and post-operatively to visibly ascertain its condition, location and efficacy.
g) To be implantable permanently, retrograde and be able to completely obliterate a false lumen of a dissection and to maintain patency of the main lumen as well, as the patency of all side branches throughout its length.
Other reference publications:
1. Self-Expanding Metalic Stents for Small Vessels Radiology 1987 162.469-472.
2. Flexible Balloon-Expandable Stent for Small vessels, Radiology, January 1987.
3. Intravascular Stents to Prevent Occlusion and Restenosis After Transluminar Angioplasty, N.E.J. of M., Mar. 19, 1987.
4. U.S. Pat. No. 4,580,568, Percutaneous Endovascular Stent.
5. U.S. Pat. No. 4,503,569, Transluminarely Placed Expandable Graft Prosthesis, Dotter 1985.
6. U.S. Pat. No. 4,649,992, Catheter Arrangement Having a Variable Diameter Tip and Spring Prosthesis, Wiktor 1987.
7. U.S. Pat. No. 4,681,110, Catheter Arrangement and Blood Vessel Liner, Wiktor 1987.
All of the above references describe and teach various methods of providing or otherwise offering and introducing stents of different types and designs for applications similar to the one described herein in this invention.
The improvement of this invention over other similar devices such as cited in patents above, and specifically my previus invention described in U.S. Pat. No. 4,649,992, is the ability of the device of this invention to allow for and to maintain a very low profile and a small frontal area, so very important for purposes of percutaneous insertion. Thus the stent of this invention can be inserted into and be transported via a standard #8F Guiding Catheter such as USCI Cat. #006128, while using standard procedures and methods. Once on location, the stent can be expanded radially to a diameter larger than initially introduced; a ratio of =2xc2xd:1 can easily be achieved with a wire diameter of 0.008 and initial stent diameter of 0.075. The expanded larger diameter will conform to the inside of the vessel and maintain intimate contact with the inside wall. The stent of this invention is characterized by the low memory level of the relatively easily deformable metal used for the wire.
The configuration of stent 1, shown in FIG. 1, is such that the wire 2 is intially preformed into a two-dimensional zig-zag form 3, basically creating a flat expandable band 3a. The zig-zag pattern can vary as to its shape and tightness of the reversing bends, but for reasons of simple description a typical sinusoidal form is chosen to depict this band""s construction.
In order to create the stent 1, and to have it assume an initial configuration as shown in FIG. 1, also a subsequently radially expanded condition as shown in FIG. 5, a length of preformed band 3a is wrapped on a suitable mandrel 4 in a manner similar to that of winding a simple helical spring again as shown in FIG. 1. Care is taken to form the wire band 3a flat around the mandrel 4 with little or no tension to prevent premature linear expansion of band 3a. 
Once the zig-zag band 3a is wound into a cylindrical shape, it is removed from the mandrel 4, and is placed over a suitable variable diameter device such as an inflatable balloon 5 typically used for angioplasty procedures as shown in FIG. 2. A suitable forming tool (not shown) is used to tighten the stent over the balloon; manual operation of squeezing the stent over the balloon is also acceptable.
A controlled radial expansion of the stent is accomplished by the force generated by the inflating balloon. When acted upon by the inflating balloon, the stent of this invention being characterized by the zig-zag preformed wire band 3a subsequently formed into an open-ended cylindrical shape, is by design and intent capable to expand radially.
The radial expansion in effect is achieved by controlled deformation and tension applied to the sinusoidal pattern of the preformed wire band 3a. The low memory metal used for the fabrication of the wire formed stent assures, that the radially expanded stent stays expanded thus fulfilling is preimary intent and function. Other advantages of this invention over those mentioned earlier Ref. 1 through 7, are the inherent post-expansion radial rigidity and linear flexibility, an excellent combination for an intravascular and especially intracoronary stent. In the case of intracoronary application, an overriding factor being the ability of allow for an extremely low profile and a very small frontal area so very essential for initial transluminar introduction and transportation through a standared 8F guiding catheter.
A major object of this invention is the provision of a preformed flexible wire stent which allows easy radial expansion and subsequent retention of the radially expanded shape well anchored within a vessel. Still anther object of this invention is the simplicity of its application, especially with respect to angioplasty, where one procedure accomplishes two distinct functions: In combination with the balloon it compresses the plaque, thus creating a recannalized lumen as characterized by angioplasty, and deploys and implants a permanent prosthesis within the newly created and recannalized lumen to prevent possible reclosure and restenosis thus allowing free flow of blood indefinitely. Both functions are performed simultaneously and with a single insertion of the catheter.
There is a need for a means to restrain an extra long stent from excessive stretching. This invention includes means for preventing a longitudinal overstretch of the stent, particularly during the initial introduction into the vessel where several constrictions occur. The introduction of the stretch limiting means guarantees a constant and uniform pitch of the helical wire formed coil throughout the entire length of the stent both in its non-expanded and especially in its expanded condition and still maintains full flexibility. The longitudinal stretch limiting means can take several forms including a straight wire placed on the outside of the tubular shaped stent spotwelded to each individual coil or alternately using a simple suture thread and tying each coil to the next. Another method found acceptable is to arrange the sinusoidal wave shape pattern where one wave shape out of a series is longer and can be bent to catch the wave of the adjacent coil.
The invention includes means for restraining coils of the helix from longitudinal movement relative to each other. In other words, means are provided for restraining lengthwise stretch of the coil. To one embodiment, the means includes a single lengthwise wire attached, for example, by welding to loops of the coil. In another embodiment, the loop of the coil is hooked over an adjacent loop to restrain longitudinal movement.